This is an anti-static duster, that is a useful tool to remove excess powder from your DTF film. Static electricity, humidity and other environmental factor can affect your DTF film such that it can adhere to more powder than is necessary. Sometimes these factors (especially static) can cause your powder to adhere to the film even in areas where there is no printing / ink. Leaving the powder on the film before you heat the film and before you press the film to your shirt, can result in specs of powder adhering to your shirt and show up as specs of white. The use of an anti-static duster to dust off the excess powder helps alleviate this issue. You should still shake the powder off your film vigorously and as a first/required step, but following up with a gentle anti-static duster will help remove that last remaining stubborn powder that is clinging to the film for enviromental reasons (such as too high humidity, too low humidity, static build up or other factors).
WARNING: WORK IN A WELL VENTILATED AREA and use Protective Equipment when working with DTF products and processes as fumes may be hazardous.